The present invention relates to a liquid droplet jetting head to jet liquid from a nozzle and a liquid droplet jetting apparatus.
In a liquid jetting head to jet a liquid droplet from a nozzle such as an inkjet head (hereafter may called just head) to record an image by using a minimal ink droplet, a pressure generating device applies a pressure to a pressure generating chamber to jet the ink droplet from the nozzle so as to land the ink droplet on a recording medium like a recording sheet.
Conventionally, so called shear mode type ink jet recording head (hereinafter also called shearing mode head) has been known in which an actuator substrate is configured by forming a number of channels on a polarized piezoelectric element, a cover plate is bonded on an upper surface of the actuator substrate so as to form a number of pressure generating chambers separated by the aforesaid piezoelectric element, an electric field is applied to the piezoelectric element between the adjacent pressure generating chambers so as to deform the piezoelectric element and to jet ink from a nozzle hole formed on the cover plate or a bottom surface of the actuator substrate (Patent document 1).
Patent document 1: Japanese Patent Non-Examined Publication No. 2001-162795
In recent years, highly-functional and high quality inkjet printers are being demanded which are capable of multi step tone reproduction and resolution change, for example 300 dpi and 600 dpi to realize a high-resolution print image.
In a head disclosed in the Patent document 1, ink is jetted from the nozzle by driving the piezoelectric elements of the pressure chambers which are provided for each of nozzles one-on-one. Thus as a method to change an amount of ink droplet, it is considered that an injection amount of ink droplet is changed in accordance with driving condition such as a voltage value of a driving pulse applied to the piezoelectric element. However, usually, it was difficult to change the driving condition to a large degree so as to change a diameter of the ink droplet. In particular, it was not possible to control the amount of ink droplet without changing a speed of the ink droplet.
Further, as the other method, it is also considered that the ink droplets are shot redundantly a plurality of times for one dot by using a nozzle to jet small ink droplets and the number of shots is controlled for contrast control. In this method, a variable contrast image can be outputted consistently in a sufficiently high quality though, a decrease of a printing speed is caused since the ink jetting is carried out the plurality of times.
Also, as yet another method, it is considered that a plurality of nozzles having different ink jetting amount are disposed and combined selectively to reproduce contrast. In this case, though a level of contrast increase, there is a problem that a cost of manufacturing the head increases as the recording head becomes large.